Gekko Systems. Operations & Maintenance Training Introduction to Gravity Heia Safari Lodge - Feb 2008

Transcription

1 Gekko Systems Operations & Maintenance Training Introduction to Gravity Heia Safari Lodge - Feb 2008

2 What is of Gravity Separation? The separation of different mineral species from one another based on differences in their specific gravities using the force of gravity, which can be augmented by centrifugal force. Gold 19.3 Calcite Diamonds 3.55

3 Theory of Gravity Separation Separation by gravity depends on two factors: Settling Rate of particles Difference in Specific Gravity when compared against the medium in which they are being separated this gives differential settling rate and has been termed the Concentration Criterion Universal Magazine.. 'The Hydrostatic Balance to the Specific Gravity of fluid and solid bodies'. 1749

4 Theory of Gravity Separation Settling Rate: This is dictated by Stoke s Law = kd2g (Ds-Df) Where k is a constant, d is particle diameter, and D is SG of solid and fluid respectively.

5 Theory of Gravity Separation Concentration Criterion: Classically gravity differential ratio greater than 1.25 is required Dh Df Where Dh is sg of heavy component Dg Df Df is sg of fluid medium Dg is sg of gangue component Mineral Dh Dg Df CC Gold Diamond Ilmenite Where the higher the CC, the easier the gravity separation

6 Types of Gravity Device Gravity devices can be divided into two main groups: - Single g devices Such as Jigs, tables, sluices, spirals, These rely solely on the concentration criterion described earlier for separation - Multiple g devices Bowl Centrifugal Concentrators such as InLine Spinner Mill Liners

7 Theory of Gravity Separation Effect of increasing g force by centrifugal action Increasing G Force Settling Velocity Log Particle Size As G forces increase, settling velocity of smaller particles becomes greater

8 History of Gravity Separation Gravity separation is the oldest known mineral processing technique and is practised extensively in Nature: Placer gold deposits Alluvial and coastal diamond deposits Ilmenite in beach sands Earliest recorded human use of gravity separation was recovery of gold by panning from the Upper Nile by Nubians/Ancient Egyptians, dating back to 1900 BC

9 By Agricola s time (1556) there were many different options for gravity separation. Buddles Mills and Sluices Strakes Source: Agricola De Re Metallica, 1556

10 Advantages of Gravity Circuits Environmentally Friendly Cheap and simple to operate Gold Specific Advantages- Improves cashflow by recovering gold earlier Improves recovery due to: lower head grade to leach, no coarse gold remaining in leach Improved security no gold traps Reduced lock up (mill liners etc)

11 Illustrative Financial Benefits (Gold) Head Grade 5 g/t GRG 50% Milled Tonnage t/month CIP Recovery 98% Residence Time (CIP) 12 days Gold Price $450 /oz Interest Rate 5% Thus Conventional gold recovery = Take GRG gold out in 3 days = 980 kg/month 500 kg/month Thus accrued interest (9 days) = $ 8, per month But now get 98% recovery on CIP gold: Gold to CIP = CIP Gold recovery = Now total recovery = Or an additional Which is 500 kg/month 490 kg/month 990 kg/month 10 kg recovered per month $140, per month

12 Illustrative Financial Benefits - Diamonds Without Pre-Concentration 200 tph DMS Plant $1 per ton* $5,000 Operating Cost ($/day) $4,000 $3,000 $2,000 $1,000 $0 With Pre-Concentration 200 tph IPJ Plant at $0.20 per ton** 50 tph DMS Plant at $0.93 per ton Overall operating cost of $0.43 per ton precon feed DMS IPJ *Estimated by Bateman **Actual Site Data

13 Potential Disadvantages of Gravity Separation Increased circuit complexity Production of valuable concentrates can be a security risk (but prevents concentrate being produced in uncontrolled areas!) Due to the nature of the concentrates can be difficult to sample and account for. Typical cost of running a gravity circuit, concentrators and intensive leach estimated at US$1 /oz recovered

14 Typical Layouts & Equipment Options (Diamonds) 1: Conventional DRAFT FLOWSHEET - DIAMONDS - Conventional Option Oversize 300t/hr 8mm Screen 0.8mm Dense Media Plant Tailings to Heap Tailings to Heap Conc to Recovery

15 Typical Layouts & Equipment Options (Diamonds) 1: Pre Con Single Pass DRAFT FLOWSHEET - DIAMONDS - Option 2 300t/hr Oversize 8mm Screen 75t/hr/IPJ 0.8mm Screen IPJ2400 IPJ2400 IPJ2400 IPJ2400 Tailings to Heap 225t/hr Tailings to Heap 75t/hr Conc to DMS

16 Typical Layouts & Equipment Options (Diamonds) 3: Pre Conc Rougher/Scavenger Oversize 300t/hr DRAFT FLOWSHEET - DIAMONDS - Option 3 30t/hr 330t/hr 297t/hr 8mm Screen 82t/hr/IPJ 0.8mm IPJ2400 IPJ2400 IPJ2400 IPJ2400 IPJ2400 IPJ2400 IPJ2400 IPJ2400 Tailings to Heap Tailings to Heap 267t/hr 33t/hr Conc to DMS

17 Typical Layouts & Equipment Options (Diamonds) Relative Benefits of 3 Options: Cost Centre Scenario 1 Scenario 2 Scenario 3 300t/hr DMS Plant 4 x IPJ t/hr DMS Plant 8 x IPJ t/hr DMS Plant (Note 2 Stage Jigging) Capex DMS Plant $ 3,000, $ 1,000, $ 700, IPJ Plant $ - $ 1,200, $ 2,000, TOTAL CAPEX $ 3,000, $ 2,200, $ 2,700, Opex US$/t US$/month US$/t US$/month US$/t US$/month DMS Plant Spares $ 0.76 $ 12, $ 0.08 $ 4, $ 0.15 $ 2, Labour $ 0.05 $ 9, $ 0.09 $ 4, $ 0.23 $ 4, Consumables $ 0.78 $ 154, $ 0.75 $ 37, $ , IPJ Plant $ - $ - $ 0.11 $ 22, $ 0.11 $ 44, TOTAL OPEX US$/month $ 175, $ 68, $ 70,755.53

18 Furnace Drying Ovens Typical Layouts & Equipment Options (Gold) 1: Conventional Ore Silo 1 2 SAG Thickener/Leach and CIP Plants 2 3 Splitter Drum Magnets Screen Potable Water Gravity Device Gemeni Table Drying Oven Smeltin g

19 Typical Layouts & Equipment Options (Gold) 2: Modern Conventional SAG Ball Magnetic Separators Electrowinning Bowl Centrifugal Concentrator Gold Sludge to Smelt Inline Leach Reactor To Low Grade circuit

20 Typical Layouts & Equipment Options (Gold) 3: Out of the Box BATCH ILR1000 FLOWSHEET REAGENT ADDITION SOLIDS STORAGE SOLUTION STORAGE WATER ADD SOLIDS DISPOSAL MOTOR 2.2KW REACTOR DRUM SOLUTION TO EW STORAGE MOTOR 4KW

21 Layouts and Equipment Options

22 Feed Preparation for Gravity Circuits Where does gravity circuit fit?? 1) Cyclone Underflow Most popular to date for batch units Highest grade stream Potential to increase grade via fine screening High density Coarse with a wide size distribution Lower total gold content Ensuring cut is representative

23 Feed Preparation for Gravity Circuits Where does gravity circuit fit?? 2) Cyclone Overflow Easy to get a representative cut Ideal size distribution for certain units Low tonnage/low density stream Low total gold content and low grade No second chance to collect gold Opportunity to remove coarse free gold lost

24 Feed Preparation for Gravity Circuits Where does gravity circuit fit?? 3) Mill Discharge Can be split separately from sump Highest gold content stream Lower density with slimes included aids pumping Higher water content aids screening Viscosity/slimes can affect separation Coarse with a wide size distribution

25 Feed Preparation for Gravity Circuits Efficiency of Screening? Due to the recirculation effect, loss of fines back to the circuit missing the gravity units is not a major issue What are the effects of oversize? Choking of pumps Excessive wear Blocking of process in gravity units Reduces separation efficiency Reduces recovery of fine values

26 Feed Preparation for Gravity Circuits Dilution is a double edged sword Not enough leads to minimal classification occurring Too much can destroy the water balance and hence mill efficiency

27 Feed Preparation for Gravity Circuits Magnetic Separation before gravity All milling circuits contain steel.. Originating from: Liner attrition Media breakage & attrition Underground locos, props, LHD s.. Scraper ropes and cables Etc etc etc

28 Sampling is critical to allow: Feed Preparation for Gravity Circuits Understanding of circuit performance Identification of optimum size fraction for maximum return Sampling MUST be addressed at design stage for safety, practicality etc etc!!

29 QUESTIONS?